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What formula is used to find the power cable size for a load?

Power Tools Cable Modems Power Generation
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Question added by YASIR MEHMOOD , Senior Maintenance Supervisor (Offshore UZ 750) , GISCO Facilities Services LLC
Date Posted: 2015/02/21
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Hikmat Maher Al-Wanni
by Hikmat Maher Al-Wanni , Projects Supervision Manager , 3G-ERES

Laws of resistance:

R = ρ (L/a)

ρ is the resistivity of the conductor in ohm.m, L is the length of the cable, and a is the cross sectional area of the conductor.

 

However, other methods can be used to find the proper size of the cable such as SI System and British System by using their own tables. These tables show the current required by the load and its correspond number of cables and diameter for each cable.  

Whereas the Load is known, calculate the current I in Amp as the following equation and then find its match cable size:

I= P(W)*1.2/V(Volts)

(safety margin of 20% of the Load is added)

Safi Ullah
by Safi Ullah , Electrical Trainee Engineer , PESCO (Peshawar Electric Supply Company)

I think the wire gauge is helpful.........

 

saad khan
by saad khan , Senior Deputy Manager E & I , Novatex Limited, BOPET Unit

Wire Circular mils =√3 x2 x ρ x I x L / (%Allowable Voltage drop of source voltage)   Where; ρ = Specific resistance or resistivity of Conductor D = Distance in Feet (One way) i.e. ½ the total circuit length I = Load Current Note: the Value of ρ = Specific resistance or resistivity of Conductor is used here for copper and aluminum is11.2 and17.4 respectively at 53° C (127° F)

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